(ə-rĭ'mē-ə) An abnormal rhythm of the heart, often detectable on an electrocardiogram. Electrical impulses in the heart normally originate in the sinoatrial node of the right atrium during diastole and are transmitted through the atrioventricular node to the ventricles, causing the muscle contraction that usually occurs during systole. However, abnormalities of electrical conduction during diastole or systole can result in various alterations of the heartbeat, such as changes in heart rate, skipped or irregular beats, and fibrillation of the heart muscle, which can be life threatening. These electrical disturbances can be caused by metabolic abnormalities, inadequate blood supply (as in coronary artery disease), drug effects, chronic disease, and other factors. Arrhythmias are sometimes treated with the implantation of a pacemaker.